Abstract
BackgroundThe human fungal pathogen Candida albicans is able to undergo morphogenesis from a yeast to a hyphal growth form. Protein kinase A (PKA) isoforms Tpk1 and Tpk2 promote hyphal growth in a signalling pathway via the transcription factor Efg1.ResultsC. albicans strains producing epitope-tagged Tpk1 or Tpk2 were used in genome-wide chromatin immunoprecipitation on chip (ChIP chip) to reveal genomic binding sites. During yeast growth, both PKA isoforms were situated primarily within ORFs but moved to promoter regions shortly after hyphal induction. Binding sequences for Tpk2 greatly exceeded Tpk1 sites and did not coincide with binding of the PKA regulatory subunit Bcy1. Consensus binding sequences for Tpk2 within ORFs included ACCAC and CAGCA motifs that appeared to bias codon usage within the binding regions. Promoter residency of Tpk2 correlated with the transcript level of the corresponding gene during hyphal morphogenesis and occurred near Efg1 binding sites, mainly on genes encoding regulators of morphogenesis.ConclusionsPKA isoforms change their genomic binding sites from ORF to promoter regions during yeast-hyphal morphogenesis. Tpk2 binds preferentially to promoters of genes encoding regulators of cellular morphogenesis.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2164-14-842) contains supplementary material, which is available to authorized users.
Highlights
The human fungal pathogen Candida albicans is able to undergo morphogenesis from a yeast to a hyphal growth form
C. albicans strains producing HA-tagged Protein kinase A (PKA) kinases The single remaining allele encoding the catalytic subunits of PKA kinase was modified in heterozygous C. albicans mutants to add sequences specifying a C-terminal triple hemagglutinin (HA) epitope tag
To verify that HA fusion proteins were functional in the constructed strains we tested their filamentous growth, which is known to be regulated by the activity of Tpk1 and Tpk2 proteins [2,3]
Summary
The human fungal pathogen Candida albicans is able to undergo morphogenesis from a yeast to a hyphal growth form. The cAMP-PKA pathway subsequently activates the Efg transcription factor, which represents the PKA localization differs among species: in budding yeast the PKA holoenzyme is localized in the nucleus [14], whereas in fission yeast it resides in the cytoplasm [15] and in mammalian cells PKA catalytic subunits bind to anchoring proteins in different intracellular localizations [16,17] In spite of these differences, it appears that in all species important AGC kinase activities are needed in the nucleus. Action of the Hog MAPK on the Sko trancriptional repressor required the activity of kinase Sch, which is structurally related to PKA, on the promoters of target genes [22] The latter findings suggested that in C. albicans, Tpk isoforms and possibly other kinases reside on genes that represent downstream targets of PKA signalling during hyphal morphogenesis. During the yeast-hyphal transition, genomic Tpk binding sites identify genes with known functions in dimorphism and suggest the identity of new genes involved in this cellular differentiation process
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